WSL: Provide better error message when WSL is not installed.

Signed-off-by: Mark Yen <[email protected]>

background.ts

@@ -80,6 +80,19 @@ Electron.app.whenReady().then(async() => {
   console.log(cfg);
   tray.emit('settings-update', cfg);
   k8smanager = newK8sManager(cfg.kubernetes);
+
+  // Check if there are any reasons that would mean it makes no sense to
+  // continue starting the app.
+  const invalidReason = await k8smanager.getBackendInvalidReason();
+
+  if (invalidReason) {
+    handleFailure(invalidReason);
+    gone = true;
+    Electron.app.quit();
+
+    return;
+  }
+
   imageManager = new Kim();
   interface KimImage {
     imageName: string,
@@ -486,14 +499,20 @@ async function linkResource(name: string, state: boolean): Promise<Error | null>
 }
 
 function handleFailure(payload: any) {
-  let { errorCode, message, context: titlePart } = payload;
-
-  if (typeof (payload) === 'number') {
-    errorCode = payload;
+  let titlePart = 'Starting Kubernetes';
+  let message = 'There was an unknown error starting Kubernetes';
+
+  if (payload instanceof K8s.KubernetesError) {
+    ({ name: titlePart, message } = payload);
+  } else if (payload instanceof Error) {
+    message += `: ${ payload }`;
+  } else if (typeof payload === 'number') {
     message = `Kubernetes was unable to start with the following exit code: ${ payload }`;
+  } else if ('errorCode' in payload) {
+    message = payload.message || message;
+    titlePart = payload.context || titlePart;
   }
-  console.log(`Kubernetes was unable to start with exit code: ${ errorCode }`);
-  titlePart = titlePart || 'Starting Kubernetes';
+  console.log(`Kubernetes was unable to start:`, payload);
   Electron.dialog.showErrorBox(`Error ${ titlePart }`, message);
 }
 

src/k8s-engine/hyperkit.ts

@@ -305,6 +305,10 @@ export default class HyperkitBackend extends events.EventEmitter implements K8s.
     })();
   }
 
+  getBackendInvalidReason(): Promise<K8s.KubernetesError | null> {
+    return Promise.resolve(null);
+  }
+
   async start(): Promise<void> {
     const desiredVersion = await this.desiredVersion;
 

src/k8s-engine/k8s.ts

@@ -39,6 +39,13 @@ export interface VersionLister {
   on(event: 'versions-updated', callback: ()=>void): void;
 }
 
+export class KubernetesError extends Error {
+  constructor(name: string, message: string) {
+    super(message);
+    this.name = name;
+  }
+}
+
 export interface KubernetesBackend extends events.EventEmitter {
   state: State;
 
@@ -57,6 +64,13 @@ export interface KubernetesBackend extends events.EventEmitter {
   /** The amount of memory in the VM, in MiB, or 0 if the VM is not running. */
   memory: Promise<number>;
 
+  /**
+   * Check if the current backend is valid.
+   * @returns Null if the backend is valid, otherwise an error describing why
+   * the backend is invalid that can be shown to the user.
+   */
+  getBackendInvalidReason(): Promise<KubernetesError | null>;
+
   /** Start the Kubernetes cluster. */
   start(): Promise<void>;
 

src/k8s-engine/notimplemented.js

@@ -38,6 +38,10 @@ class OSNotImplemented extends events.EventEmitter {
     return Promise.reject(new Error('not implemented'));
   }
 
+  getBackendInvalidReason() {
+    return Promise.resolve(null);
+  }
+
   start() {
     this.#notified = displayError(this.#notified);
 

src/k8s-engine/wsl.ts

@@ -209,6 +209,29 @@ export default class WSLBackend extends events.EventEmitter implements K8s.Kuber
     }
   }
 
+  async getBackendInvalidReason(): Promise<K8s.KubernetesError | null> {
+    // Check if wsl.exe is available
+    try {
+      await this.isDistroRegistered();
+    } catch (ex) {
+      if ((ex as NodeJS.ErrnoException).code === 'ENOENT') {
+        console.log('Error launching WSL: it does not appear to be installed.');
+        const message = `
+          Windows Subsystem for Linux does not appear to be installed.
+
+          Please install it manually:
+
+          https://docs.microsoft.com/en-us/windows/wsl/install-win10
+        `.replace(/[ \t]{2,}/g, '');
+
+        return new K8s.KubernetesError('WSL Not Installed', message);
+      }
+      throw ex;
+    }
+
+    return null;
+  }
+
   async start(): Promise<void> {
     try {
       if (this.process) {